One conventional belt driving device for use in image forming apparatuses includes a fixing belt stretched over a pair of rollers, the fixing belt having a pair of block bodies integrated with respective inner circumferences of a pair of side edge portions of the fixing belt along a circumferential direction thereof. An axial end portion of the roller is made into a tapered surface. When the fixing belt is likely to lean to either side of the axial direction of the roller, the block body of the fixing belt comes into contact with an end portion forming the tapered surface of the roller, by which leaning of the fixing belt is regulated (FIG. 4B in JP 2002-182501A).